ABSTRACT

Gels are cross-linked networks of polymers swollen with a liquid. Two-thirds of the human body consists of water, and almost all known biological reactions occur in water. The ability of polysaccharides to form a network structure, even at very low concentrations, constitutes one of their most important functional properties. Many natural and bacterial polysaccharides, charged or uncharged, form three-dimensional networks under specific conditions. Cross-linking is one of the oldest methods for the chemical modification of polymers. Various degrees of cross-linking can be introduced into polysaccharides for the purpose of generating larger molecular aggregates with enhanced viscosity profiles, or for the preparation of insoluble products with a wide range of swelling characteristics. Reaction of polysaccharides with epichlorohydrin usually leads to cross-linking, but monofunctional side reactions may also occur to form a series of by-products with glycolic functional groups.